Field of the Invention
The present invention relates to a load drive apparatus which includes an application voltage control section for applying to an electrical load a pulse voltage alternately assuming a high potential and a low potential and which drives and controls the electrical load.
Description of Related Art
An example of a load drive apparatus which drives and controls an electrical load such as a heater for heating a gas detection element is one having an application voltage control section for applying to the electrical load a pulse voltage alternately assuming a high potential and a low potential.
In such a load drive apparatus, there may occur various anomalous states such as a short-to-ground anomalous state in which opposite ends of an electrical load are connected to the ground potential (GND potential) and a wire breakage anomalous state in which an energization path for applying a pulse voltage to the electrical load is broken.
In view of this, there has been proposed an apparatus which has a function of judging whether or not there has occurred the short-to-ground anomalous state of the electrical load or the wire breakage anomalous state of the energization path (Patent Document 1). Namely, Patent Document 1 discloses an apparatus which measures the power supply voltage of a heater when the heater is operated and when the heater is not operated and which outputs a corresponding failure signal when the difference between the measured values of the power supply voltage is less than a predetermined minimum value or greater than a predetermined maximum value.
Meanwhile, as a result of long-term use, the electrical characteristics of the electrical load may change, and the electrical load may come into a deteriorated state. However, the apparatus disclosed in Patent Document 1 cannot detect such a deteriorated state of the electrical load.
In order to overcome such a drawback, there has been proposed an anomaly detection apparatus which judges a deteriorated state of an electrical load through use of a current detection resistor (shunt resistor) which is connected in series to the electrical load and in parallel to a switching element of the application voltage control section (Patent Document 2). Notably, the switching element is provided as a portion of the application voltage control section. The application voltage control section is provided so as to switch the conduction state of an energization path extending from a power supply to the electrical load by turning the switching element on and off, to thereby control the voltage applied to the electrical load.
Namely, in this anomaly detection apparatus, when the supply of electricity to the electrical load by the application voltage control section is stopped, a deteriorated state of the electrical load is judged on the basis of the current of the electrical load detected through use of the current detection resistor.